1. Field of the Invention
This invention relates to method and apparatus for lowering the suspension on a vehicle and more particularly to apparatus for relocating the leaf springs of the suspension below the axle housing to lower the frame where the load supporting the leaf springs is transferred from the axle to a mounting assembly surrounding the axle housing.
2. Description of the Prior Art
In a conventional suspension system for a vehicle leaf springs are utilized to support the axle housing on the vehicle frame so that when the wheel strikes minor obstacles in the road the shock forces are transmitted through the axle to the springs. The springs then serve to dampen the vibration that is transmitted to the vehicle body.
The leaf springs are connected to the frame adjacent the rear wheels of the vehicle. The opposite ends of the springs are connected by tension-type shackles or brackets to the vehicle frame. The leaf springs are positioned above the axle housing. The springs are connected to the axle housing by a hanger assembly that includes in one embodiment a pair of U-bolts that are positioned on opposite sides of the leaf springs and extend upwardly around the axle housing into a bolted connection with an anchor plate. The anchor plate extends in overlying relation with the leaf springs and is connected to the vehicle frame.
In certain applications it is desirable to lower the vehicle frame with respect to the axle housing. This is accomplished by decreasing the vertical distance between the vehicle frame and the axle housing so as to lower the floor height of the vehicle. This is advantageous in a vehicle such as a bus to make it easier for passengers to enter and exit the bus. Lowering the frame of a vehicle is also desirable in the customization of vehicles, such as trucks, so that the frame ground clearance is lower to provide desired aesthetic affects.
In order to decrease the distance between the vehicle frame and the axle housing it is necessary to relocate the leaf springs from above the axle housing to a position below the axle housing. This requires a modification in the hanger assembly for connecting the leaf springs to the axle housing. Apparatus for supporting leaf springs below the axle housing are well known in the art. One example is disclosed in U.S. Pat. No. 2,868,538 where the leaf springs of the vehicle suspension are mounted below and clamped to the axle housing by U-bolts which pass around the axle and extend through the top plate of an angle clamp and a bottom plate. Nuts on the ends of the U-bolts are tightened against the bottom plate. The leaf springs are compressed by a bolt passing through the plate at the top and the plate at the bottom of the springs. In a similar arrangement U.S. Pat. No. 4,342,469 discloses in a trailer suspension system leaf springs mounted below an axle by U-bolts and retaining plates.
In U.S. Pat. No. 3,494,609 a spring beam is coupled to an axle housing by U-bolts. The bolts straddle the axle housing and a pressure plate is positioned at the bottom of the spring beam through which the legs of the U-bolt pass. Nuts are tightened on the U-bolt against the pressure plate. Italian Pat. No. 647561 discloses leaf springs clamped below the axle between a pair of pressure plates. Legs of a U-bolt pass through the pressure plates, and nuts on the end of the U-bolt are tightened to compress the leaf spring between the pressure plates.
In U.S. Pat. No. 3,103,349 an axle housing is secured to leaf springs by a set of four bolts that pass through a pair of brackets, an upper plate, and a lower plate so as to secure the brackets and the plates together about the leaf springs. The upper and lower plates are positioned beneath the axle housing by shackles.
U.K. Pat. Application No. 2,141,677A discloses a vehicle lowering suspension system for buses in which bolts are used to clamp together upper and lower plates to secure the leaf springs to the axle housing. U.S. Pat. Nos. 2,258,449; 3,285,281; 3,861,708; and 4,966,387 are further examples of leaf suspension systems in which the leaf springs are supported by U-bolts beneath the axle housing.
A problem is encountered with a lowering suspension system in which the leaf springs are supported by U-bolts beneath the axle housing. The U-bolts have a tendency to slip on the axle because the tops of the U-bolts do not sit squarely on the axle. Slippage or lateral movement of the U-bolts has been known to dislodge the mounting of the leaf springs on the axle, causing damage to the axle.
In a vehicle lowering suspension system, the vertical distance between the vehicle frame and the top of the axle housing is decreased. This reduces the clearance for movement of the axle housing relative to the vehicle frame. In order to accommodate the decreased distance between the vehicle frame and the top of the axle housing the vehicle frame is provided with a C-section above the axle to increase the clearance at the point where the axle passes beneath the frame. This allows for upward and downward travel of the frame without interfering with the axle housing.
In a further effort to dampen movement of the axle housing a shock absorber is mounted on opposite ends of the axle housing adjacent the vehicle frame. One end of the shock absorber is connected by a bracket to the axle housing and the opposite upper end of the shock absorber is connected to a bracket mounted on the vehicle frame. For the shock absorber to operate efficiently in dampening motion of the axle, the shock absorber should be positioned at 45.degree. angle with respect to the horizontal. However, when the vehicle frame is lowered with respect to the axle housing and the shock absorber is connected to the same mounting brackets on the frame and axle, the shock absorber is positioned at an angle less than 45.degree. and approaches a horizontal position. At an angle substantially less than 45.degree. the shock absorber will not operate properly to dampen motion transmitted to the vehicle frame.
Another problem encountered with lowering the suspension of a vehicle where the leaf springs are positioned below the axle housing is displacement of the drive shaft angle. In a conventional suspension system where the leaf springs are positioned above the axle housing the drive shaft extends at an angle of approximately 6.degree. below the horizontal. With conventionally known vehicle lowering suspension systems positioning the leaf springs below the axle housing and decreasing the vertical distance between the vehicle frame and the axle housing raises the drive shaft to a position that is substantially horizontal. Raising the drive shaft to this degree is known to result in vibration or "chatter" of the drive shaft placing undue wear on the connections from the crank shaft to the universal joint.
While it is known in vehicle lowering suspension systems to decrease the clearance between the vehicle frame and axle housing by positioning the leaf springs below the axle housing the prior art devices utilize U-bolts that extend into overlying contact with the axle housing and into connection with a spring plate to hang the leaf springs below the axle housing. This arrangement creates undesired loading of the axle housing. It also places undesirable stress on the drive shaft because it dislocates the angle of the drive shaft. Also, adjustments must be made to connect the shock absorbers at the desired operational angle between the vehicle frame and axle housing.
Therefore, there is need in a vehicle lowering suspension system to support the leaf springs below the axle housing in a manner that removes the load from the axle housing and maintains the drive shaft as close as possible to the preferred angle extending between the crank shaft and the universal joint.